Device for generating electric sparks for igniting flammable vapors containing gas and air

ABSTRACT

A spark generating device is described comprising a condenser connected to spaced electrodes forming a spark gap and electrically polarized elements rotatably disposed for charging the condenser.

United States Patent Bauser et a1.

[ Dec. 16, 1975 DEVICE FOR GENERATING ELECTRIC SPARKS FOR IGNITING FLAMMABLE VAPORS CONTAINING GAS AND AIR Inventors: Herbert Bauser, Friedrichsdorf;

Dieter Fischer, Frankfurt am Main, both of Germany Assignee: Braun Aktiengesellsehaft, Frankfurt am Main, Germany Filed: July 19, 1974 Appl. No.: 490,213

Foreign Application Priority Data July 23, 1973 Germany 2337347 US. Cl. 317/81; 307/88 ET; 29/592; 317/96; 431/255 Int. Cl. F23Q 3/01 Field of Search 317/81, DIG. 11; 29/592, 29/594; 136/164; 307/88 ET, 108;

References Cited UNITED STATES PATENTS 1/1968 Rabe 317/81 3,384,786 5/1968 Oyamada et a1 3l7/8l X 3,444,435 5/1969 Hzllm 317/81 3,517,206 6/1970 Oliver 307/88 ET X 3,550,257 12/1970 Brown et al. 29/592 3,748,727 7/1973 Swain 307/88 ET X 3,817,694 6/1974 Makino 431/255 OTHER PUBLICATIONS The Physics Teacher, Vol. 9, No. 3, Mar. 1971, Electrostatic Motors Jefimenko et al., pp. l21129.

T. A. Dickinson, Electrets, Plastic Research Co. pp. 1 & 20-24.

Primary Examiner -volodymyr Y. Mayewsky Attorney, Agent, or Firm-Frederick E. Bartholy [5 7] ABSTRACT A spark generating device is described comprising a condenser connected to spaced electrodes forming a spark gap and electrically polarized elements rotatably disposed forcharging the condenser.

1 Claim, 3 Drawing Figures US. Patent Dec. 16,1975 Sheet10f2 3,927,354

fi -J.

Sheet 20f 2 1 3,927,354

U.S. Patent Dec. 16, 1975 tive energy transfer utilizing a transformer and battery supply are well known in the art.

These devices have various drawbacks. Some require continuous attention others. an energy source in-the form of a battery. The cost of manufacturing them may 'also'be' quite high. 2 v1 1 -The primary object of the invention is to provide an ignition device which requires-no depletable source of energy, and is free from service maintenance.

It is a feature of the invention that the ignition device hereunder may be manufactured at relatively low cost.

It is a particular advantage of the invention that the ignition device is small in size so that it can be incorporated into pocket-size cigarette lighters.

Other objects, features and advantages will be apparent from the following description of the invention, pointed out in particularity in the appended claims, taken in connection with the accompanying drawings in which:

FIG. l-a is a schematic representation of an electrical circuit utilizing an electret as the charging element with the latter in a position about to be inserted between conductive plates.

FIG. l-b is a circuit similar to that of FIG. l-a showing the electret in the inserted position.

FIG. 2 is an exploded view in perspective illustrating a practical embodiment for use in pocket-size lighters.

An electret is a permanently polarized piece of dielectric material analogous to a magnet. Ceramics, such as barium titanate, can be so polarized under certain conditions when subjected to an electric field. Electrets are also produced by solidification of mixtures of certain organic waxes in a strong electric field. They may be produced in the form of thin disk-shaped dielectric materials and retain their polarization for an extended time some over years. Consequently, they outlive the normally useful life of any mechanical assembly in which they may be incorporated, for example, in cigarette lighters.

Referring to the drawings, the principle of operation is illustrated in FIGS. La and H2.

An electret l is about to be inserted between two conducting plates, such as metal plates 2a and 2b. These plates are conductively connected to a condenser C which is in parallel with two ball-shaped electrodes 5a and 5b forming the spark gap 4.

The insertion creates a charge on plates 2a and 2b of a polarity opposite to that of the polarization of the electret 1. Since the circuit components, namely, 2a and 2b, 3, C, 5a and 5b we re originally not charged, the induced charge on plates 2a and 2b results in charges opposite to that of the electret. If this charge is sufficiently high to produce an electric field which breaks down the air resistance between the electrodes 5a and 5b, the opposite charges discharge in the form of a spark between the electrodes. However, the induced charge on plates 20 and 2b remains unaltered. By sufficient charge and electrical energy, the resultant spark will ignite a mixture of flammable gas and air.

When the electret is pulled out again, the induced charges on plates 20 and 212 will build up a charge on 2 t condenser C. The dischargeythereof will be dissipated in the form ofa spark. In this manner, the original rest conditionis re-establi'shed. I

The energy of the spark is created by the mechanical work necessary to establish the separation of! the charges. It is known that, in order to ignite a combustible gas-air mixture, not only the electrical energy of the spark is important, but also that the magnitude of the current transfer plays avery important role. For dependable ignition of a stream of butane-air vapor, it is necessary to have a current of approximately 3.2 microamperes. The ignition potential difference, in order to serve the purpose, would be about 8 kilovolts. From this it is seen that the electrical energy required is N=QXU=3.2 l0 '8 l0 W=25 l0 while the minimum spark energy of the usual ignitable gas-air mixtures is in the neighborhood of 0.20.3 l0 W. v

A good electret in air can be charged to about 10' amp/cm and, in inert gas such as SP to SXIO amp/cm If we take a charge of 2 l0 amp/cm it is necessary for the storage of the required charge of 3.2 l0 to have a surface of 160 cm The capacitance of the charged condenser must be The above-stated conditions permit the design, in accordance with the invention, of a compact cigarette lighter mechanism as illustrated in FIG. 2. The electret l is in the form of a disk of which the electrical polarization of one-half is opposite to that of the other half. Above and below the electrets are placed divided metal disks 2 of which each half is electrically insulated from the other half. These are similarly interconnected by conductor 3 with condenser C and spark gap 4.

The electret is rotatable over an axis 6 while the metal plates are solidly affixed to supports 7.

In the starting condition there will be no induced charge on the metal disks inasmuch as each half lays between oppositely charged quarter segments of the electrets. However, when the electret is turned then each disk half lays over a particular polarized portion of the electret. In this manner, each disk half receives an induced charge of opposite polarity to that of the segment of the electret. Over the conductors 3 of the similarly charged disk halves 2, there develops an opposite charge on the condenser and between poles of the spark gap, the total charge of opposite polarity. It is seen from FIG. 2 that a spark will be created at every 90 rotation of the electret.

In a practical embodiment, in order to have sufficient spark energy to ignite the gas escaping from a tank, eight electrets and nine metal disks are used. The diameter of the disks is 5 cm. Thus, a parallel connection represents a total surface area of cm The thickness of each electret is 0.2 mm and the thickness of the metal disks is 0.04 mm. In total, these disks form a roll having a thickness of 0.08 mm. The electrets are within this roll so that there is an air space of 0.02 mm between the disks and the electrets. In this manner, losses due to friction are eliminated. In addition, charges due to static electricity are minimized.

The total thickness of this construction is 8 X 0.2mm 9 X 0.9mm 2.4mm.

The condenser C consists of a metallized plastic of 0.15 mm thickness. If the plastic has a dielectric con- 3 stant of E 3, the capacitance of the condenser will be C 400 pF. j

As seen in FIG. 2, this condenser, including a dielectric of 0.15mm thickness, is mountedon the assembly so that the total thickness of the igniter is 2.7mm. With a diameter of 5cm, a space of 5.4cm is needed. The anchoring of the spark gap will take another cubic centimeter so that the total volume of the igniter is around 65cm. This arrangement is sufficiently compact to fit any pocket lighter.

The invention in its broader aspects is not limited to the specific embodiments herein shown and described but changes may be made within the scope of the accompanying claims without departing from the principles of the invention and without sacrificing its chief advantages.

What is claimed is:

l. A device for generating an electric spark for the ignition of gas-air mixtures comprising a circuit including a condenser, a pair of electrodes connected bewhereby, upon rotation of said electrets, said sets of 7 disk members receive a charge of opposite polarity, causing a cumulative charge transfer on said condenser, resulting in a spark discharge between said pair of electrodes. 1 

1. A device for generating an electric spark for the ignition of gas-air mixtures comprising a circuit including a condenser, a pair of electrodes connected between terminals of said condenser forming a spark gap, a pair of conductive plates connected between said terminals, a plurality of electrets in the form of thin disks rotatably supported on a shaft, each disk having a segment of one polarity and another segment of a polarity opposite thereto comprising two sets of semi-circular disk members insulated from each other, one of said sets being connected to one terminal of said condenser and the other set to the other terminal thereof whereby, upon 90* rotation of said electrets, said sets of disk members receive a charge of opposite polarity, causing a cumulative charge transfer on said condenser, resulting in a spark discharge between said pair of electrodes. 